U.S. patent number 4,239,506 [Application Number 05/703,942] was granted by the patent office on 1980-12-16 for use of aqueous, non-sweep liquid during membrane separation.
This patent grant is currently assigned to Standard Oil Company (Indiana). Invention is credited to Robert D. Hughes, Edward F. Steigelmann.
United States Patent |
4,239,506 |
Steigelmann , et
al. |
December 16, 1980 |
**Please see images for:
( Certificate of Correction ) ** |
Use of aqueous, non-sweep liquid during membrane separation
Abstract
A material is separated from a fluid mixture by contacting the
mixture containing the material with a first side of essentially
solid, water-insoluble, hydrophilic, semi-permeable membrane in
contact with an aqueous liquid barrier having ions which combine
with the material to be separated to form a water-soluble complex.
The partial pressure of the material on a second side of the
semi-permeable membrane is sufficiently less than the partial
pressure of the material in the mixture to provide separated
material on the second side of the membrane. The separated material
can be removed from the vicinity of the second side of the membrane
by a gas stream. The second side of the membrane is contacted with
an aqueous liquid medium to reduce the loss of the aqueous liquid
barrier from the membrane which may otherwise decrease in
separation efficiency during use due to water losses. The gas
stream used to remove the separated material may be supersaturated
with the aqueous medium, e.g. water, and may contact the membrane
with the aqueous medium via condensation. Alternatively, the
aqueous medium such as water may be applied by a continuous or
intermittent film, spray or mist. The process is particularly
useful for separating olefins, especially ethylene.
Inventors: |
Steigelmann; Edward F.
(Naperville, IL), Hughes; Robert D. (Naperville, IL) |
Assignee: |
Standard Oil Company (Indiana)
(Chicago, IL)
|
Family
ID: |
24827409 |
Appl.
No.: |
05/703,942 |
Filed: |
July 9, 1976 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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498112 |
Aug 16, 1974 |
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Current U.S.
Class: |
95/44;
210/651 |
Current CPC
Class: |
B01D
53/22 (20130101); B01D 61/38 (20130101); C07C
7/152 (20130101); C07C 7/152 (20130101); C07C
11/04 (20130101) |
Current International
Class: |
B01D
53/22 (20060101); B01D 61/38 (20060101); C07C
7/00 (20060101); C07C 7/152 (20060101); B01D
059/10 () |
Field of
Search: |
;210/23F,23H
;55/16,158 |
References Cited
[Referenced By]
U.S. Patent Documents
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|
|
3758603 |
May 1973 |
Steigelmann et al. |
3812651 |
September 1973 |
Steigelmann |
|
Primary Examiner: Therkorn; Ernest G.
Attorney, Agent or Firm: Bernard & Brown
Parent Case Text
This is a continuation of application Ser. No. 498,112, filed Aug.
16, 1974, now abandoned.
Claims
It is claimed:
1. In a process for separating an aliphatically-unsaturated
hydrocarbon from a fluid mixture comprising
contacting said mixture containing said aliphatically-unsaturated
hydrocabon with a first side of an essentially solid,
water-insoluble, hydrophilic semi-permeable membrane having therein
an aqueous liquid barrier having metal-containing ions which
combine with said aliphatically-unsaturated hydrocarbon to form a
water-soluble complex,
the partial pressure of said aliphatically-unsaturated hydrocarbon
on a second side of the semi-permeable membrane being sufficiently
less than the partial pressure of said aliphatically-unsaturated
hydrocarbon in said mixture to provide the separated
aliphatically-unsaturated hydrocarbon on the second side of the
semi-permeable membrane,
removing said separated aliphatically-unsaturated hydrocarbon from
the vicinity of the second side of the semi-permeable membrane, the
improvement comprising contacting the second side of the
semi-permeable membrane with an aqueous, non-sweep liquid medium
during said aliphatically-unsaturated hydrocarbon separation in an
amount sufficient to reduce the loss of water from said aqueous
liquid barrier during said separation.
2. The process of claim 1 wherein said fluid mixture is
gaseous.
3. The process of claim 1 wherein the aliphatically-unsaturated
hydrocarbon contains 2 to 4 carbon atoms.
4. The process of claim 3 wherein said separated
aliphatically-unsaturated hydrocarbon is removed from the vicinity
of the second side of the semi-permeable membrane by a
substantially inert gas stream.
5. The process of claim 4 wherein the substantially inert gas
stream is supersaturated and contact with the aqueous medium is
achieved by condensation onto the second side of the semi-permeable
membrane as the substantially inert gas stream removes said
separate aliphatically-unsaturated hydrocarbon.
6. The process of claim 5 wherein the substantially inert gas
stream is saturated at an elevated temperature and then cooled to
supersaturation.
7. The process of claim 3 wherein the second side of the
semi-permeable membrane is contacted with aqueous medium as a
continuous liquid phase film during the separation process.
8. The process of claim 3 wherein said mixture is a mixture of
ethylene and low molecular weight paraffins and said separated
material is ethylene.
9. The process of claim 3 wherein said membrane comprises a
polyamide membrane and said metal-containing ions are
silver-containing ions.
10. The process of claim 9 wherein said polyamide is an
N-methoxymethyl polyamide.
11. The process of claim 9 wherein said membrane further comprises
polyvinyl alcohol.
12. The process of claim 11 wherein said membrane is comprised of
hollow fibers.
13. The process of claim 9 wherein said membrane is comprised of
hollow fibers.
14. The process of claim 13 wherein said polyamide is an
N-methoxymethyl polyamide.
15. The process of claim 14 wherein said membrane further comprises
polyvinyl alcohol.
16. The process of claim 14 wherein said mixture is a mixture of
ethylene and low molecular weight paraffins and said separated
material is ethylene.
17. The process of claim 13 wherein said second side of the
semi-permeable membrane is the outside of said hollow fibers and it
is contacted with aqueous medium as a continuous liquid phase
film.
18. In a process for separating a material from a fluid mixture
comprising
contacting said mixture containing said material with a first side
of an essentially solid, water-insoluble, hydrophilic
semi-permeable membrane having therein an aqueous liquid barrier
having metal-containing ions which combine with said material to
form a water-soluble complex,
the partial pressure of said material on a second side of the
semi-permeable membrane being sufficiently less than the partial
pressure of said material in said mixture to provide separated
material on the second side of the semi-permeable membrane,
removing said separated material from the vicinity of the second
side of the semi-permeable membrane by a substantially inert gas
stream, the improvement comprising contacting the second side of
the semi-permeable membrane with an aqueous, non-sweep liquid
medium during said material separation in an amount sufficient to
reduce the loss of water from said aqueous liquid barrier during
said separation.
19. In a process for separation a material from a fluid mixture
comprising
contacting said mixture containing said material with a first side
of an essentially solid, water-insoluble, hydrophilic
semi-permeable membrane having therein an aqueous liquid barrier
having metal-containing ions which combine with said material to
form a water-soluble complex,
the partial pressure of said material on a second side of the
semi-permeable membrane being sufficiently less than the partial
pressure of said material in said mixture to provide separated
material on the second side of the semi-permeable membrane,
removing said separated material from the vicinity of the second
side of the semi-permeable membrane with a sweep stream having less
than a sweeping amount of aqueous liquid medium or with vacuum, the
improvement comprising contacting the second side of the
semi-permeable membrane with an aqueous, non-sweep liquid medium
during said material separation in an amount sufficient to reduce
the loss of water from said aqueous liquid barrier during said
separation.
Description
This invention relates to an improved process for separating a
material from a fluid mixture containing it by utilizing
metal-complexing techniques employing an essentially solid,
water-insoluble, hydrophilic, semi-permeable membrane in contact
with an aqueous liquid barrier containing ions which combine with
the material to be separated to form a water-soluble complex. In
the process the loss of water from the membrane is materially
reduced by contacting the surface of the membrane from which the
separated material leaves the membrane, i.e., the exit surface,
with an aqueous liquid medium while the separation proceeds. The
separated material can be removed from the vicinity of the exit
surface of the membrane by, for example, a sweep gas stream.
There is considerable commercial interest in separating components,
e.g., aliphatically-unsaturated hydrocarbons, from mixtures
containing such materials. These aliphatically-unsaturated
hydrocarbons are reactive materials that serve in various roles in
chemical syntheses. A number of the unsaturated hydrocarbons are
employed as monomers in the formation of polymers and, in this
regard, olefins such as ethylene, propylene, butadiene and isoprene
are well known. These olefins, as well as other unsaturated
materials, for instance, acetylene, are also used to form
relatively low molecular weight products.
The aliphatically-unsaturated hydrocarbons are most often made
available on a commerical basis in admixture with other chemical
compounds, frequently other hydrocarbons. These unsaturated
hydrocarbon-containing streams are usually by-products of chemical
syntheses or separation processes. When the hydrocarbon streams are
liquid under normal conditions or can readily be made so, ordinary
distillation techniques can be used to separate the hydrocarbon
components, providing they have sufficiently different boiling
points for the process to be economically feasible. Especially when
the hydrocarbon mixtures contain materials having close boiling
points, which is frequently the case with hydrocarbons of the same
number of carbon atoms or having a difference of only one carbon
atom, distillation may not be an attractive separation procedure.
In such cases, more expensive processes are often used and involve
operations such as solvent extraction or extractive distillation
which entail considerable expense, if indeed they are technically
feasible in a given situation.
When the mixture containing the aliphatically-unsaturated
hydrocarbon is essentially in a gaseous state at normal or ambient
conditions of temperature and pressure, separation of the desired
component from the mixture may be even more troublemsome. In these
situations, cryogenic processes may be used, but they are
expensive. The components of these normally gaseous mixtures may
not even have particularly close boiling points, but, nevertheless,
the mixture must be cooled in order to separate one or more of its
components. In spite of the considerable cost of cryogenic
operations, the procedure has been employed commercially for the
separation of ethylene from other gaseous materials such as ethane
and methane.
Several of our patents and pending patent applications described
methods for separating materials such as aliphatically-unsaturated
hydrocarbons and carbon monoxide, from mixtures containing them,
and these procedures involve the combined use of liquid barrier
permeation and metal-complexing techniques which can exhibit high
selectivity factors. In the processes, the liquid barrier is an
aqueous solution having metal-containing ions which will complex
with the material to be separated, and the liquid barrier is
employed in conjunction with a semi-permeable membrane which is
essentially impermeable to the passage of liquid. In several
systems of this type, the liquid barrier containing the
complex-forming ions is in contact with the membrane and preferably
is at least partially contained in a hydrophilic, semi-permeable
film membrane. When operating in this preferred manner, it is not
necessary to maintain contact of the film with a separate or
contiguous aqueous, complex-forming, liquid phase during the
process, and this may facilitate the use of a greater variety of
semi-permeable members as far as physical configuration is
concerned. Thus, the membranes can be designed without having to
provide a separate liquid phase adjacent the inlet side of the
membrane film, and this may enable the use of membrane
configurations having a greater surface or contact area. Such a
separate liquid phase may, however, be employed. The film membranes
can be essentially homogenous materials which are suitable for
forming into various shapes, and the membranes may be formed by,
for instance, extrusion and can be made into hollow fiber forms.
These fibers are preferred membrane configurations because they
have the advantages of high surface area per unit volume, thin
walls for high transport rates, and high strength to withstand
substantial pressure differentials across the membrane or fiber
walls.
This invention is directed to an improved process of these types in
which a material is separated from a fluid mixture by utilizing an
essentially solid, water-insoluble, hydrophilic, semi-permeable
membrane having therein an aqueous liquid barrier containing ions
which combine with the material to be separated to form a
water-soluble complex, and during the separation, an aqueous liquid
medium, i.e., an aqueous, non-sweep liquid medium, e.g. water in
the liquid phase, with or without other constituents, is provided
on the exit surface of the membrane from a source extraneous to the
membrane to decrease water loss from the film and thereby enhance
the operation of the separation system. In the process a material
is separated from a feed mixture by contacting the latter with a
first side of the membrane while having a partial pressure of the
material on a second or exit side of the semi-permeable membrane
which is sufficiently less than the partial pressure of the
material in the mixture to provide separated material on the second
side of the membrane. The separated material can be removed from
the vicinity of the second side of the membrane by, for instance, a
sweep gas. By the process of this invention, the loss of water from
aqueous liquid barrier in the membrane is materially reduced and
decreases in permeability and selectivity during operation are
thereby minimized. Similar results were not obtained when the feed
mixtures and sweep gas are merely saturated with moisture.
Typically the amount of the aqueous liquid medium contacted with
the surface of the membrane from its exit side as the separation
proceeds is sufficient to retard water loss from the membrane. Such
amounts may vary depending upon the type of membrane and operating
conditions, and generally sufficient of the aqueous liquid medium
is supplied to retard or prevent crystallization of the
metal-containing ionic component from the liquid barrier solution.
In one preferred embodiment of this invention, a supersaturated gas
stream is used to remove the separated material from the exit side
of the membrane, and water is deposited onto the exit side of the
membrane by condensation from the supersaturated gas stream. The
supersaturated sweep gas flow rate may be chosen to adequately
remove the separated material from the vicinity of the exit or
discharge side of the membrane, and the extent of supersaturation
may be determined based on water losses and on the chosen sweep gas
flow rate. Suitable temperatures for the sweep gas may be about
40.degree. to 120.degree. F., preferably about 70.degree. to
110.degree. F. It is preferred that sufficient aqueous medium be
contacted with the exit side of the membrane to maintain the water
content of the membrane substantially constant during the
separation and to thus maintain a substantially constant
concentration of complexing ions in solution during the
separation.
The supersaturated sweep gas stream is preferably a gas which is
relatively inert to reaction with the material separated, and the
gas may be supersaturated by any suitable means. For example, the
gas may be heated, saturated with water and then appropriately
cooled to create a supersaturated gas. Other supersaturation
techniques may be used such as pressure change supersaturation
methods. Various methods may be used to contact the
water-containing gas stream with the discharge side of the membrane
employed in the separation process at the desired temperature,
flow, and supersaturation conditions.
In a preferred embodiment of this invention, the aqueous medium
contacts the exit side of the membrane by liquid aqueous medium
discharge. For example, sprays, mists, flowing streams, films, or
other liquid forms can be employed near or at the membrane exit
side to permit liquid discharge onto the exit side of the membrane.
The water discharge rate should be sufficient to adequately
decrease aqueous liquid barrier losses from the membrane and may be
continuous or intermittent. For example, a fine mist of aqueous
medium may be continuously directed onto the exit side of the
membrane or an intermittent stream may be discharged whenever, for
instance, separation selectivity or permeability drops below a
desired value. These processes may include automatic control which
measures selectivity or permeability and is set to initiate a
discharge of a predetermined quantity of aqueous medium whenever
the measured condition drops below a predetermined level.
Alternatively, intermittent discharge may be based on a
predetermined or set frequency or time period.
Whenever the membrane is contacted with the aqueous medium by
direct liquid discharge, it is desirable to substantially saturate
or humidify the sweep gas stream to avoid having the sweep gas
capture the deposited moisture. However, this substantial
saturation or humidification of sweep gas may be accomplished in
the vicinity of the membrane as, for example, simply by including
sufficient aqueous medium in the spray or other discharge means so
as to substantially saturate or humidify the sweep gas. The aqueous
medium is essentially water but may include other components such
as complexing ion components, e.g. silver nitrate. Additionally,
the aqueous medium may contain other separation enhancing
components such as, for example, hydrogen peroxide, as more fully
described in commonly-assigned copening application, Ser. No.
512,972, filed on Oct. 7, 1974, now U.S. Pat. No. 4,014,665.
In another embodiment of the present invention, a vacuum is used to
remove the separated material. In this embodiment the aqueous
medium can be deposited by liquid discharge means, as discussed
above. The vacuum is maintained so as to adequately remove the
separated material, but is not so great as to have an undue
detrimental effect on the aqueous medium contact to the membrane
surface. Generally, a vacuum may be used to adequately remove the
separated material, but to avoid aqueous medium losses by suction.
The vacuum pressure is chosen such that the partial pressure of the
material to be separated on the low pressure side of the membrane,
i.e., the exit side, is less than that of the material to be
separated on the high pressure or inlet side.
In one preferred embodiment of the present invention, the exit side
of the membrane surface is contacted with a continuous liquid phase
film of the aqueous medium, i.e., the exit side surface is kept
substantially completely wetted. This may be accomplished by either
continuous or intermittent delivery of aqueous medium to the
continuous liquid phase film by various of the above-mentioned
techniques. In the system in which hollow fibers are used as the
membranes, the continuous liquid phase aqueous medium film may be
advantageously used when the feed to be separated is passed through
the inside of the fibers and the separated material exits from the
outside of the fibers. When the continuous liquid phase aqueous
medium film is employed, the separated material may be removed from
the exit side of the membrane by, for instance, bubbling sweep gas
through the liquid phase aqueous medium film.
The membranes employed in the process of the present invention are
hydrophilic at least to some extent and include those membranes
which contain additional hydrophilic and/or hygroscopic agents, and
those that do not. A film membrane may be considered hydrophilic if
it absorbs at least about 5 weight percent of water when immersed
in distilled water for one day at room temperature and pressure.
Typical membranes are those formed of film-forming materials such
as nylon, e.g., the N-alkoxyalkyl polyamides, and those formed of
nylon and more hydrophilic polymers such as polyvinyl alcohol,
polyvinyl ethers, polyacrylamides and the like. The membrane
materials may be formed into single membrane structures of desired
configuration, as for example, by casting, or they may be formed
into hollow fibers by hot melt extrusion and subsequently "bundled"
into an array with potting compounds. The hollow fiber membranes
are preferred because they provide the greatest surface contact
area, and when the feed gas passes through the inside of the
fibers, the cylindrical configuration provides a greater surface
area on the exit side than on the inlet side which may promote
separated gas transfer to the exit side. Additionally, surprisingly
exceptional separation is achieved with the hollow fiber membranes
when the feed gas is passed to the outside of the fibers and the
sweep gas is passed through the inside of the fibers and the
separated material passes from the outside to the inside of the
hollow fibers, particularly when the outside of the fibers is
flooded with the liquid barrier solution.
Regardless of the particular membrane configuration employed in the
process of this invention, it is desirable to arrange the membrane
so as to avoid uneven distribution of the contacting aqueous medium
by gravity. In processes in which a flat membrane is essentially
vertically positioned, it is preferable to contact the exit side of
the membrane with the aqueous medium at its highest point so that
gravity will favorably distribute the aqueous medium over the
surface of the exit side. The vertical flat membrane may be tilted
so as to assure that the aqueous medium "flows" into the membrane.
Alternatively, the flat membrane may advantageously be placed in a
horizontal position with the exit side facing upwardly. When fibers
are used as the membrane and are situated to run generally
horizontal they may be tilted with the segment which is first
contacted with the aqueous medium as the higher end to assure that
it runs down the length of the outside of the fibers. This may also
be achieved by arranging the fibers in a vertically mounted
position.
In the separation process the liquid barrier contains a metal
component which provides ions capable of forming a complex with the
materials desired to be separated from a mixture. The source of the
ions may be added to the film or be mixed with the polymer or
film-forming constituents prior to formation of the film. The
complex-forming component may be impregnated into the film in an
aqueous or other form and when impregnated in aqueous form may or
may not contain water in an amount sufficient to establish the
aqueous liquid barrier used in the separation process. In any
event, the membrane has sufficient water to form the aqueous liquid
barrier when used in the separation process.
The amount of water in the liquid barrier employed may be a minor
portion of the liquid phase, but preferably is a major portion or
even substantially all of the liquid, on a metal compound-free
basis. Thus, small or minor amounts of water, say as little as
about 5 weight percent, on a compound-free basis in the liquid
phase may serve to provide significant transport across the liquid
barrier of the material to be separated. Any other liquid present
in the barrier is preferably water-miscible and should be chosen as
not to have a substantial deleterious effect on the separation to
be accomplished. The liquid barrier may also contain a hygroscopic
agent, e.g., in a minor amount, to improve the wetting or
hydrophilic properties of the liquid and provide better contact
with the feed gas.
The membrane containing the complex-forming metal may be handled
and transported in an essentially non-aqueous form or with some
water therein, for instance, an insufficient amount of water to be
effecitve in the separation. In such case, water would be added to
the membrane to give a film bearing sufficient water to be useful
in performing the separation process. However, the membrane may
tend to dry during use even when the membrane contains major
amounts of hydrophilic polymers. This drying generally results in a
considerable decrease in permeability and in selectivity for the
separation and is counteracted by the process of this
invention.
The process of the present invention may be employed to separate,
for instance, one or more unsaturated hydrocarbons by the liquid
barrier-complex-forming technique in which the barrier is at least
partly contained in the membrane. Although the separated products
provided may be quite pure materials, for instance, of greater than
99% purity, the separation procedure may be used merely to provide
significant increase in the concentration of a given material in a
mixture with other components of the feedstock.
The process can be employed to separate various materials from
other ingredients of the feed mixture providing at least one of the
materials exhibits a complexing rate or transfer rate across the
liquid barrier that is greater than at least one other dissimilar
or different component of the feedstock. Quite advantageously, the
system can be used to separate aliphatically-unsaturated
hydrocarbons from other hydrocarbons which may be
aliphatically-saturated or aliphatically-unsaturated, or from
non-hydrocarbon materials, including fixed gases such as hydrogen.
The feed mixture may thus contain one or more paraffins, including
cycloparaffins, mono- or polyolefins, which may be cyclic or
acyclic, and acetylenes or alkynes, and the mixture may include
aromatics having such aliphatic configurations in a portion of
their structure. often, the feed mixture contains one or more other
hydrocarbons having the same number of carbon atoms as the
unsaturated hydrocarbon to be separated or only a one carbon atom
difference. Among the materials which may be separated according to
this invention are ethylene, propylene, butenes, butadiene,
isoprene, acetylene and the like.
In the method, the mixture containing the material to be separated
may be essentially in the gaseous or vapor phase when in contact
with the liquid barrier having dissolved therein one or more
metal-containing ions which form a complex with the material to be
separated. The liquid barrier can be essentially entirely within
the semi-permeable membrane which may be permeable to the mixture
in the absence of the liquid barrier. The membrane can be said to
somewhat immobilize the liquid barrier within the membrane and the
membrane in the presence of the liquid barrier is selective to the
passage of the component of the feedstock to be separated. Since
there is little, if any, passage for the feedstock across the
separation zone except by becoming part of or reacting with the
liquid barrier, this liquid barrier controls the selectivity of the
liquid barrier-semi-permeable membrane combination. Since the water
content of the liquid barrier is maintained at a desired operating
level in the process of this invention, high selectivity and
permeability are thereby assured.
The liquid barrier contains sufficient water and soluble
metal-containing ions to form a suitable complex with at least one
component of the feed subjected to the separation procedure. The
metal ions form the complex upon contact with the feed, and, in
addition, the complex dissociates back to the metal-containing ion
and a component of the complex which was in the feed, under the
conditions which exist on the discharge side of the liquid barrier
and semi-permeable membrane as employed in the process. The
released feed component exits the discharge side of the membrane
and can be removed from the vicinity of the barrier and its
supporting structure as by a sweep gas or through the effect of
vacuum on this side of the barrier as discussed above. Thus the
metal complex forms and is decomposed in the complex metal
ion-containing liquid barrier, and, as a result, the material
passing through the barrier is more concentrated with respect to at
least one component present in the feed stream.
Often, the reactivity of aliphatically-unsaturated hydrocarbons
with the complexing metal ions in their order of decreasing
activity goes from acetylenes or dienes to monoolefins, the
aliphatically-saturated hydrocarbons and other materials present
being essentially non-reactive. Also, different reactivities may be
exhibited among the various members of a given type of
aliphatically-unsaturated hydrocarbon. The process can thus be used
to separate paraffins from monoolefins, diolefins or acetylenes;
diolefins from monoolefins; or acetylenes from paraffins,
monoolefins or diolefins; as well as to separate a given
aliphatically-unsaturated hydrocarbon from another of such
materials in its class where the members have differing complexing
rates with or transport rates across the liquid barrier. The feed
need only contain a small amount of aliphatically-unsaturated
hydrocarbon, as long as the amount is sufficient so that the
unsaturated material to be separated selectively reacts with the
metal-containing ions to a significant extent, and thus at least
one other component of the feed is less reactive or non-reactive
with the complex-forming metal ions.
The aliphatically-unsaturated materials of most interest with
regard to separation have 2 to about 8 carbon atoms, preferably 2
to 4 carbon atoms. The separation of aliphatically-unsaturated
materials from admixtures containing other gaseous materials, such
as the separation of ethylene or propylene from admixtures with
other normally gaseous materials, e.g., one or more of ethane,
propane, methane and hydrogen, is of particular importance.
Frequently, such feed mixtures for the process contain about 1 to
50 weight percent ethylene, about 0 to 50 weight percent ethane and
about 0 to 50 percent methane. Another process that may be of
special significance is the separation from ethylene of minor
amounts of acetylene.
The partial pressure of the material in the feed to be separated is
at the input side of the liquid barrier used in the separation,
greater than the partial pressure of this component on the
discharge or exit side of the liquid barrier-semi-permeable
membrane composite. This pressure drop across the membrane of the
material to be separated may often be at least about 0.5 pound per
square inch, and is preferably at least about 20 psi, although the
pressure drop should not be so great that the liquid barrier is
ruptured or otherwise deleteriously affected to a significant
extent. Conveniently, the total pressure of the feed is up to about
1000 pounds per square inch. The partial pressure of the separated
material upon discharge from the membrane can preferably be
controlled by subjecting the exit side of the liquid barrier to the
action of a sweep gas that may be essentially inert to forming a
complex with the metal ions in solution in the liquid barrier. The
sweep gas picks up the discharged or separated components of the
feed, and the sweep gas may be selected so that it can be readily
separated from the discharged components if that be necessary for
the subsequent use of the latter. Unless a reaction with the
separated material is desired, the sweep gas should be relatively
inert therewith and may be, for instance, butane, carbon dioxide or
the like.
The temperature across the liquid barrier-semi-permeable membrane
composite employed in the separation procedure can be essentially
constant or it may vary, and decomposition of the metal complex can
be effected primarily by the drop in partial pressure of the
material to be separated on the exit side of the liquid barrier
compared with its partial pressure on the feed side. Conveniently,
the temperature of the liquid barrier may be essentially ambient,
especially in the case of feedstocks that are gaseous at this
temperature and the pressure employed on the feed side of the
liquid barrier. The temperature of the liquid barrier may, however,
be reduced or elevated from ambient temperature. Often, the
temperature may be up to about 100.degree. C., and elevated
temperatures may even be desired to put the feedstock in the
gaseous or vapor phase. Neither the temperature nor the pressure
used should, however, be such as to destroy the difference in
transport rate across the liquid barrier, semi-permeable film
composite, of the material whose separation is sought, compared
with that of the other components of the feed. The conditions
should also not be such that physical disruption of the liquid
barrier or any other significant malfunction results.
The materials which can be employed to make the semi-permeable film
membranes of the present invention may be of the hydrophilic types
that have been heretofore employed for the separation or
purification of various chemical materials. Among these hydrophilic
film-forming materials are those disclosed in U.S. Pat. Nos.
3,228,877 and 3,566,580, incorporated herein by reference. Most
advantageously, however, the materials employed may have a
film-forming N-alkoxyalkyl polyamide as an essential component. The
polyamide film-forming materials are generally known and have also
been designated as nylons. The polymers are characterized by having
a plurality of amide groups serving as recurring linkages between
carbon chains in the product structure, and the polymers may be
made by several procedures. Commonly, the polyamides are formed by
reacting a polyamine and a dicarboxylic acid or its derivative such
as an ester, especially a lower alkyl ester having, for instance,
about 1 to 4 carbon atoms in the ester group. Other reactions which
may be employed to form the polyamides include the
self-condensation of monoamino, monocarboxylic acids and the
reactions of cyclic lactams. In any event, the polyamide products
contain recurring amide groups as an integral part of the principle
polymer chain. The polyamides are described, for instance, in the
Kirk-Othmer, Encyclopedia of Chemical Technology, Second Edition,
Volume 16, beginning at page 1, Interscience Publishers, New York,
1968. Among the typical structural formulas of the linear
polyamides are H.sub.2 NRNH (COR'CONHRNH).sub.n COR'COOH and
H.sub.2 NRCO (NHRCO).sub.n NHRCOOH, where R and R' represent
primarily carbon-to-carbon chains between functional groups in the
reactants, and n represents the degree of polymerization or the
number of recurring groups in the polymer chain. The polyamides
which can be used in this invention are generally solid at room
temperature, and have a molecular weight which makes them suitable
for forming the desired membranes.
The carboxylic acids which may be used in forming the polyamides
have an acyloxy group (--R--COO--) in their structure and the R
member of this group is composed essentially of carbon and hydrogen
and often contains about 6 to 12 carbon atoms. Such groups may be
aliphatic, including cycloaliphatic, aromatic, or a mixed structure
of such types, but such groups are preferably aliphatic and
saturated with respect to carbon-to-carbon linkages. These R groups
may preferably have straight chain carbon-to-carbon or normal
structures. Among the useful dicarboxylic acid reactants are adipic
acid, sebacic acid, azelaic acid, isophthalic acid, terephthalic
acid, and the methyl esters of these acids.
The polyamines employed in making the polyamides generally have at
least two non-tertiary, amino nitrogen atoms. These nitrogen atoms
may be primary or secondary in configuration, although amines
having at least two primay nitrogen atoms are preferred. The
polyamides may also have both primary and secondary nitrogen atoms
and the polyamines may contain tertiary nitrogen atoms. The
preferred polyamine reactants have aliphatic, including
cycloaliphatic, structures, and often have from 2 to about 12
carbon atoms. Also, the preferred polyamines are saturated and have
straight-chain structures, although branched-chain polyamines can
be used. Among the useful polyamines are ethylene diamine,
pentamethylene diamine, hexamethylene diamine, diethylene triamine,
decamethylene diamine and their N-alkyl substituted derivatives,
for instance, the lower alkyl derivatives which may have, for
instance, 1 to 4 carbon atoms in the alkyl substituents.
The polyamide polymers which can be employed with particular
advantage in this invention include those in which the film-forming
polyamide is an N-alkoxyalkyl-substituted polyamide. Materials of
this type are well known, as shown, for instance, by U.S. Pat. Nos.
2,430,910 and 2,430,923, which disclose N-alkoxymethyl polyamides
made by the reaction of a polyamide polymer, formaldehyde and
alcohol. Generally, at least about 5% of the amide groups of the
polymer are substituted with alkoxyalkyl groups and such
substitution may be up to about 60% or more. Preferably, this
substitution is about 10 to 50% with the product being soluble in
hot ethanol.
The alcohols employed in making the N-alkoxyalkyl polyamides are
generally monohydric and may have, for instance, from 1 to about 18
or more carbon atoms. The lower alkanols are preferred reactants,
especially the lower alkanols having 1 to 4 carbon atoms. Among the
useful alcohols are methanol, propanols, butanols, oleyl alcohol,
benzyl alcohol, lauryl alcohol and alcohol ethers, for instance,
the alkyl ethers of ethylene glycol.
The N-alkyloxyalkyl polyamides which can be employed in the present
invention to provide a desired semi-permeable membrane may be
reacted with cross-linking agents. The cross-linking agents may be,
for example, polycarboxylic acids, especially the dicarboxylic and
tricarboxylic acids which may have, for instance, from 2 to about
12 carbon atoms. Useful acids include oxalic acid, citric acid,
maleic acid, and the like.
Film-forming membranes which can advantageously be employed in the
present invention can be made by intimately combining, by either
physical means or through chemical reaction, the N-alkoxyalkyl
polyamide and a hygroscopic polymer material, e.g., the
water-soluble polyvinyl alcohols. The polyamides and hygroscopic
polymer may be used as a physical admixture or in various reacted
forms, for instance, as cross-linked polymers or block or graft
copolymers. The hygroscopic polymer is generally employed in an
amount sufficient to enhance the hydrophilic properties of the
polyamide and may be up to about 75 weight % or somewhat more of
the membrane composition based on the total polyamide and
hygroscopic polymer, and the latter is often at least about 5 or
15% and the amount is sufficient to impart a significant property
to the film-forming combination. Preferably, each of the
hygroscopic polymer and the polyamide are about 25 to 75% of their
combination or total amount, or the hydroscopic polymer may be
about 35 to 55% and the polyamide about 45 to 65% of their
combination.
The polyvinyl alcohols which can be employed in the membranes used
in the present invention are essentially water-soluble materials,
at least in hot water, and many of these are commercially
available. The molecular weights of these polymers are often at
least about 1000, and are commonly in the range of about 10,000 to
300,000. Suitable polyvinyl alcohols are described in, for example,
"Water-Soluble Resins," Second Edition, Edited by Robert L.
Davidson and Marshall Sittig, pages 109 to 115, Reinhold Book
Corporation, New York, New York. The polyvinyl alcohol may be
cross-linked, especially after membranes are formed from the
polymeric materials. The presence of the cross-linked polyvinyl
alcohol may increase the strength of the fibers or other membranes
and increase their resistance to loss of polyvinyl alcohol by
leaching during use. The polyvinyl alcohol may also be cross-linked
by reaction with formaldehyde, e.g., by immersing the fibers in an
aqueous bath containing 40% (NH.sub.4).sub.2 SO.sub.4 and 10% HCHO
and 71/2% H.sub.2 SO.sub.4, at 50.degree. C. for 1 to 3 hours.
The film membranes of this invention may advantageously be made
from a mixture-containing nylon, polyvinyl alcohol, di (lower
alkyl) sulfoxide, and water as more fully described in copending
U.S. patent application Ser. No. 419,091 filed on Nov. 26, 1973,
and incorporated herein by reference.
The film membranes which can be employed in this invention are
preferably self-supporting and have sufficient strength not to
require any additional supporting material on either of its sides
during use. With some films, however, it may be necessary,
advantageous or convenient to provide adequate support such as
additional film or sheet-like materials on one or both sides of the
film membrane. These supporting structures are frequently very thin
materials and may be permeable to both liquids and gases and not
serve a separating function with respect to any component of the
feed stream. Alternatively, the supporting film may be permeable to
gases, but not to liquids.
The film membranes may be in the form of flat disc-like films, for
example, or may be extruded membranes in the form of thin hollow
fibers. In flat form the film membranes may have a thickness of up
to about 30 mils or more. Preferably the thickness is up to about
10 or 15 mils. The films are sufficiently thick to avoid rupture
during use and generally have a thickness of at least about 0.05
mil. In one preferred embodiment the membranes are formed by
extrusion into thin walled fibers.
A suitable process for extruding the fibers involves providing the
mixture having an elevated temperature suitable for extrusion, for
instance, a temperature of about 60.degree. to 125.degree. C.,
preferably about 70.degree. to 110.degree. C. The material is
extruded to form fibers having a hollow core surrounded by the
membrane wall. During extrusion it is advantageous to pass a gas
through the core of the hollow fibers to help cool the fibers and
prevent the core of the fibers from closing. After extrusion the
fibers can be dried to remove solvents and other low boiling
materials. The resulting membranes have sufficient thickness so as
not to be readily ruptured or otherwise undergo physical
deterioration at a rate that would make their use unattractive.
Generally the thickness of the fiber wall may be up to about 30
mils or more, preferably about 0.5 to 15 mils, and often the
thickness is at least about 0.1 mil. The overall diameter of the
fiber may usually be up to about 75 mils, preferably about 1 to 30
mils.
The properties, for instance, the strength and permeability, of the
membrane fibers may be improved by drawing or stretching them and
this can be accomplished at ambient or elevated temperatures.
Suitable elevated temperatures include about 90.degree. to
300.degree. C., preferably about 125.degree. to 200.degree. C. The
fibers may also be annealed at such temperatures, and the
stretching and annealing may be accomplished simultaneously. The
drawn fibers have a reduced overall diameter and thinner walls than
before stretching whether at ambient or elevated temperature, and
this treatment may preferably increase the length of the fibers by
a factor of at least about 1.25, say up to about 10 or more. This
treatment may decrease the thickness of the walls to where they are
less than about 0.5 of the thickness they had before stretching.
Excessive stretching may adversely affect the strength and
performance of the fibers and thus we prefer that their length may
not be increased by a factor of more than about 9. The stretching
of the fibers is preferably accomplished when they are swollen with
an aqueous or organic liquid. The swelling agent is preferably
water. The amount of swelling agent present during stretching is
often a minor amount up to about 50 weight percent of the fiber,
preferably is at least about 1 weight percent.
In the present invention, the metals in the film or in the liquid
barrier solution, which metals may serve in the form of
metal-containing cations to separate a component from a mixture
through the formation of metal complexes of desired properties,
include, for instance, the transition metals of the Periodic Chart
of Elements having atomic numbers about 20. Included in these
metals are those of the first transition series having atomic
numbers from 21 to 29, such as chromium, copper, especially the
cuprous ion, manganese and the iron group metals, e.g., nickel and
iron. Others of the useful complex-forming metals are in the second
and third transition series, i.e., having atomic numbers from 39 to
47 or 57 to 79, as well as mercury, particularly as the mercurous
ion. Thus, we may employ noble metals such as silver, gold and the
platinum group, among which are platinum, palladium, rhodium,
ruthenium and osmium. The useful base metals of the second and
third transition series include, for example, molybdenum, tungsten,
rhenium and the like. Various combinations of these complex-forming
metals may also be employed in this invention, either in the
presence or absence of other non-metal or non-complexing metal
components.
The metal is provided in the film or in the aqueous liquid barrier
of the separation system in a form which is soluble in this liquid.
Thus, the various water-soluble salts of these metals can be used
such as the nitrates and halides, for instance, the bromides and
chlorides, fluoborates, fluosilicates, acetates, carbonyl halides
or other salts of these metals which can serve to form the desired
water-soluble complexes when the film is in contact with water. The
metal salts should not react with any components of the chemical
feedstock used in the separation procedure to form an insoluble
material which could block the film membrane or otherwise prevent
the separation of a component from the feedstock. Also, in a given
system, the metal is selected so that the complex will readily
form, and yet be sufficiently unstable, so that the complex will
decompose and the dissociated material leave the liquid barrier,
thereby providing a greater concentration of the material to be
separated from the exit side of the membrane than is in the feed.
The concentration of the metal ions in the film or liquid barrier
may be rather low and still be sufficient to provide an adequate
complexing rate so that excessive amounts of the semi-permeable
membrane surface will not be needed to perform the desired
separation. Conveniently, the concentration of the complex-forming
metal ions in the aqueous solution forming the liquid barrier is at
least about 0.1 molar and is preferably about 0.5 to 12 molar.
Advantageously, the solution is less than saturated with respect to
the complex-forming metal ions to insure that essentially all of
the metal stays in solution, thereby avoiding any tendency to plug
the film membrane and destroy its permeability characteristics.
When the complexing ions in the liquid barrier employed in this
invention include cuprous ions, ammonium ions can be used to
provide copper ammonium complex ions which are active to form a
complex with the material to be separated by the use of the film.
We preferably supply about equimolar amounts of cuprous and
ammonium ions, although either type of ions may be in excess. The
ammonium ions can be provided in various convenient ways,
preferably as an acid salt such as ammonium chloride or as ammonium
hydroxide or ammonium carbonate. In order to enhance the
selectivity of the copper ammonium ion complex in the separation of
this invention, we may also make the film and thus the liquid
barrier solution more acidic, by, for instance, providing a
water-soluble acid such as a mineral acid, especially hydrochloric
acid in the film or liquid barrier solution. Preferably, the pH of
the liquid barrier in this form of the invention is below about 5
with the acid in the solution. Since silver may form undesirable
acetylides with acetylenes, the copper ammonium complex may be a
more attractive complexing agent when it is desired to use the film
to separate acetylenes from various mixtures.
Instead of supplying only a noble metal for complexing the material
to be separated in the process of this invention, we may also
employ mixtures of noble metal and other cation-providing
materials. A portion of the noble metal may be replaced by
non-noble metal or ammonium components. Accordingly, the total of
such ion-forming materials in the film or in the liquid barrier may
be composed of a minor or major amount of either the noble metal or
the non-noble metal, ammonium or other components. Solutions having
a major amount of the non-noble metal, ammonium or other
cation-providing materials not containing a noble metal will
generally be less expensive, and, accordingly, the noble metal may
be as little as about 10 molar percent or less of the total
cation-providing material in the solution. To reduce expenses, at
least about 10 molar percent, preferably at least about 50 molar
percent, on a cation basis of the total, of a cation-providing
material may be other than noble metal. The non-noble or base
metals are preferably of Groups II to VIII of the Periodic Chart of
Elements, and especially those in the fourth and fifth periods,
aluminum and magnesium. Zinc and copper ions are preferred ones
among these non-noble or base metal components. The various metals
may be provided in the liquid barrier in the form of any suitable
compound, such as the acid salt forms mentioned above with respect
to the noble metals.
In the system of the present invention, the amount of
complex-forming metal in the semi-permeable membrane may vary
considerably, but is sufficient to accomplish the desired
separation. Often, this is a minor amount, say, about 1 to 50
weight percent, of the weight of the membrane on a non-aqueous
basis, preferably about 5 to 25 weight percent. A suitable
procedure for placing the solution of complex-forming metal in the
semi-permeable film is by contacting the film with the solution and
exerting a differential pressure across the solution and film.
Thus, the pressure behind the solution is greater than that on the
opposite side of the film, and as a result, the solution is forced
into the film under pressure. Conveniently, the pressure of the
solution is above atmospheric, and the opposite side of the film is
essentially at atmospheric pressure. The pressure differential need
not be large, for instance, it may only be at least about 5 or 10
psi, and it should not be so great that the film is ruptured.
This invention will be further illustrated by the following
specific examples.
EXAMPLE I
Dry fibers having an inner diameter of 0.021 inches and an outer
diameter of 0.033 inches and containing 30 wt. % polyvinyl alcohol
(Borden's 0 to 0.5% acetate, average molecular weight of about
12,360 as determined by gel permeation), and 70 wt. % nylon
(Belding, BCI-819, a methoxymethyl 6:6 nylon) are formed by
extrusion from a mixture of 14.3 wt. % polyvinyl alcohol, 33.3 wt.
% nylon, and 47.6 wt. % of a 4.8 wt. % water in dimethyl sulfoxide
solvent solution. After extrusion, the fibers are dried at
75.degree. C. for two hours, cross-linked at 50.degree. C. for one
hour in a bath containing 5% Na.sub.2 SO.sub.4 and 3% p-toluene
sulfonic acid, washed three times with distilled water and
dried.
Ten of the fibers each having an effective length of about 11
inches, are bundled into an array using Dow Sylgard 184 potting
agent at each end. This produces a total surface area of about 46.8
cm.sup.2 based on the fiber inner diameter. In the separation unit
the hollow fibers were arranged in an array within a glass tube.
Feed gas containing the material to be separated entered one end of
the inside of the hollow fibers and raffinate exited the other end
of the fibers. The separated material passed from the inside of the
hollow fibers to the outside and was removed from the vicinity of
the fiber membranes by a sweep gas passing along the outside of the
fibers.
In this example, the fibers are impregnated by soaking in aqueous 2
N AgNO.sub.3 for fifteen minutes and then are rinsed with acetone
and placed in the glass tube. A feed mixture containing 15.3%
methane, 44.7% ethane, and 40.0% ethylene and having a relative
humidity of about 50% is fed through the inside of the hollow
fibers at a pressure of 20 psig and a flow rate of 10 ml./min. A
relatively dry nitrogen purge or sweep gas at atmospheric pressure
is passed through the glass tube around the outside of the hollow
fibers at a rate of 10 ml./min.
In this example, no water is deposited on the outside of the fiber
membranes after initial impregnation with silver nitrate solution
and during five days of continuous operation the permeation rate
drops from a start-up rate of 35.times.10.sup.-4 ml./cm..sup.2 min.
down to 10.times.10.sup.-4 ml./cm..sup.2 min. At the end of six
days, the permeation rate is down to zero.
EXAMPLE II
The separation unit and procedure of Example I are again used, but
the hollow fibers from Example I are reimpregnated with a 4 N
AgNO.sub.3 solution for thirty minutes. Gas feed and sweep gas
conditions are the same as in Example I but both the feed and sweep
gases have a relative humidity of about 100% instead of 50%. No
water is deposited on the outside of the membranes. As in Example
I, the permeation rate drops to about zero after six days of
continuous operation.
EXAMPLE III
The separation unit and procedure of Example I are again used and
the fibers from Example II exhibiting a permeation rate of about
zero are first soaked in distilled water for two minutes and then
employed in the separation process continuously until permeability
again approaches zero. At this time an embodiment of the process of
this invention is used. The temperature of the humidifier for the
nitrogen purge gas is raised to 60.degree. C. and the line between
the humidifier and the inlet to the separation unit is heated to
prevent condensation. As the purge gas reaches the fibers, which
are at about 24.degree. C., excess water condenses onto the outside
of the fibers and causes the ethylene permeation rate to increase
slowly. The performance levels are shown in Table 1 below. At the
end of six days of continuous operation with water being deposited
on the membrane the permeability has leveled off at about
25.times.10.sup.-4 ml./cm..sup.2 min. and the percent ethylene in
the product has leveled off at about 97.5%.
TABLE 1. ______________________________________ Permeability %
Ethylene Day of Continuous ml./cm..sup.2 min. in Operation (.times.
10.sup.-4) Product ______________________________________ 1 11 2
about 90 2 4 about 92.5 3 7 about 94.5 4 16 97.5 5 27 97.8 6 24
97.6 7 -- 98.1 8 -- 97.0 ______________________________________
EXAMPLES IV-VI
As examples of different modes of operation of the invention, the
following Examples IV-VI were performed:
Fibers were prepared from a polymer mixture containing 180 gms
BCI-819 nylon (Belding Chemical Industries), 120 gms polyvinyl
alcohol (DuPont's Elvanol 71-30), 270 ml dimethyl sulfoxide, and 30
ml water. The mixture was extruded through an annular die
(O.D.=0.030" and I.D.=0.014"). The polymer was pumped through the
outer portion at the rate of 12 ml/min while air was pumped through
the inner part at the rate 0.38 ml/min. In this manner a fiber was
produced which had an O.D. of 0.0237" and an I.D. of 0.0072".
During the extrusion, the fiber was quenched in an acetone bath for
at least 30 min, and then air dried. The nylon polymer was
cross-linked by immersing the fibers in a bath containing 3%
p-toluene sulfonic acid and 5% Na.sub.2 SO.sub.4 at 50.degree. C.
for 1 hour. Following this, the fibers wery washed three times in
distilled water to remove any of the remaining cross-linking bath
salts.
Next, the fibers were oriented by passing them through a 4-foot
long tube furnace at 80.degree. C. and at the rate of 3 feet/min.
While they were passing through the furnace, they were stretched
with a 200 gm weight. After this orientation they were annealed at
170.degree. C. for 10 min while under no stress. The final fibers
had an O.D. of 0.0215" and an I.D. of 0.0055".
Six 19" sections of this fiber were potted into a unit using
Sylgard (Dow) 184 encapsulating agent. After the potting was
completed 12" of active length for each fiber and a total fiber
area for the unit of 18.4 cm.sup.2 were obtained between potting
joints.
This unit was tested under three different modes of operation, all
with the feed on the outside of the fiber at 100 p.s.i.g. and at a
flow of 2 ml/min and with a helium purge stream on the inside of
the fiber at about atmospheric pressure and at a flow of 2 ml/min.
For example IV, the shell side of the bundle was filled with a 6 N
AgNO.sub.3 +0.3% H.sub.2 O.sub.2 solution, and a 0.3% H.sub.2
O.sub.2 solution was trickled through the length of the fibers at
the rate of 0.0019 ml/min. For Example V, the shell side was filled
with a 6 N AgNO.sub.3 +0.3% H.sub.2 O.sub.2 solution, and a 4 N
AgNO.sub.3 +0.3% H.sub.2 O.sub.2 solution was trickled through the
length of the fibers at the rate of 0.0016 ml/min. For Example VI,
the shell side was free of solution and a 4 N AgNO.sub.3 +0.3%
H.sub.2 O.sub.2 solution was trickled through the length of the
fibers at the rate of 0.0016 ml/min.
The results of this test and the number of days for each mode are
given in accompanying Table 2. The results show that operation for
all three modes is comparable and that good permeation rates may be
maintained for many days of operation by maintaining the gas exit
side of the membrane with a supply of water.
TABLE 2.
__________________________________________________________________________
Comparison of Methods for Operating Membrane Unit (Feed Pressure =
100 psig; Feed Rate = 2 ml/min; Purge Rate = 2 ml/min) No. of
Permeation Days on Product Rate Unit Stream Wt % CH.sub.4 Wt %
C.sub.2 H.sub.4 Wt % C.sub.2 H.sub.6 ml/cm.sup.2 min
__________________________________________________________________________
Feed -- 20.59 40.13 39.28 -- Example IV (6 N AgNO.sub.3 8 0.32
99.26 0.42 .00208 + 0.3% H.sub.2 O.sub.2 outside and 0.3% H.sub.2
O.sub.2 inside) Example V (6 N AgNO.sub.3 7 0.40 98.99 0.61 .00174
+ 0.3% H.sub.2 O.sub.2 outside and 4 N AgNO.sub.3 +-0.3% H.sub.2
O.sub.2 inside) Example VI (nothing 9 0.34 99.17 0.49 .00184
outside and 4 N AgNO.sub.3 + 0.3% H.sub.2 O.sub.2 inside)
__________________________________________________________________________
* * * * *